1. Field of the Invention
The present invention relates to a control circuit for an actuator, and more particularly to a control circuit for an actuator which is used to switch the area of an oil passage in a shock absorber of a variable damping force type suspension system.
2. Discussion of Background
Various actuators have been devised heretofore to adjust the rotational position of a switching rod of a variable damping force type shock absorber for vehicles. One known arrangement as disclosed in e.g. Japanese Examined Utility Model Publication No. 24850/1987 is to include a bar-shaped permanent magnet which is fixed to an output shaft of an actuator, and a stator which has a plurality of pairs of electromagnets arranged so as to be circumferentially spaced from each other outside of the opposite ends of the permanent magnet, the electromagnets in each pair being symmetrically positioned to each other with respect to the center of the output shaft. One pair of the electromagnets is selectively excited to attract the permanent magnet, thereby rotating the output shaft.
As stated above, the conventional actuator has such an arrangement that one pair of the electromagnets which are arranged at the position where the permanent magnet is desired to stop are excited in the direction of attracting the permanent magnet, thereby to stop the permanent magnet by magnetic attraction. Such arrangement creates a problem wherein it is difficult to stop precisely the permanent magnet just at a desired stopping position due to a decrease in torque at a location adjacent to the desired stopping position, and a friction load of the shock absorber.